Limonene carbonyl compound reduction

Catalytic transfer reduction of carbonyl compounds. Aryl aldehydes and ketones are completely reduced by transfer of hydrogen from cyclohexene or limonene catalyzed by 10% Pd-C and a Lewis acid (FeCla, AICI3, even HaO). Alcohols are intermediates. ... 

An additional methodology for the selective reduction of unsaturated acyclic and cyclic carbonyl compounds is composed of refluxing for 15-45 minutes a mixture of limonene and the enone substrate in the presence of 10% Pd/C. For example, the reduction of /3-octalone afforded the cis isomer in 83% selectivity, which is comparable to the results obtained with hydrogen (Scheme 3 and 5) and ammonium formate (Scheme 19). The high yields and selectivity as well as the no need for an acid or basic medium makes this method very convenient. 

Aromatic aldehydes and ketones are reduced to the corresponding hydrocarbons in good yield by catalytic transfer reduction using cyclohexene or limonene as a donor, palladium-carbon as catalyst and a Lewis-acid promotor such as ferric chloride. The major competing reaction is decarbonylation, otherwise the reaction is straightforward and simply involves heating the catalyst, carbonyl compound, and donor under reflux for 3—5 h, furthermore the method is convenient and dispenses with elaborate equipment or potentially explosive hydro n. ... 

However, in this section, the total synthesis of yingzhaosu A, the lead compound of a particular class of antimalarial 1,2-dioxocins, is reported. The synthesis involves eight steps and a 7.3% overall yield starting from (A)-limonene (Scheme 64). Besides the TOCO procedure that allowed the formation of five bonds in one step, the most intriguing steps involved the selective hydrogenation of a C-C double bond in the presence of a peroxide and an aldehyde functionalities (step vi) and the stereoselective reduction of the side-chain carbonyl with (R)-CBS catalyst (step viii). Last but not least, the old classical fractional recrystallization allowed the separation of yingzhaosu A from its C-14 epimer and saved two synthetic steps <2005JOC3618>. 

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